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In order to make accurate predictions about the fate of actinides released into the environment and to implement effective remediation strategies, fundamental studies are needed to understand the complex geochemical interactions occurring between actinides and mineral surfaces. Minerals having strong redox potentials, such as Fe and Mn oxides and oxyhydroxides, are of special interest because they are likely to influence the complex redox chemistry of Pu under groundwater conditions. Thus, the interactions of Pu(V) and Pu(VI) with the following redox active synthetic mineral phases were studied: 100% δ-MnO[sub2], 50% δ-MnO[sub2];50% α-FeOOH, and 10% δ-MnO[sub2];90% α-FeOOH (w/w). Electron microscopy data show that the δ-MnO[sub2] phases effectively coat the α-FeOOH. The binding of Pu(V) and P(VI) to sediments from the Upper Ringold Formation near the DOE Hanford Site were also investigated. Solution concentrations in the range of 1 x 10[sup-5] M to 4 x 10[sub-4] M Pu were used to minimize hydrolysis, and the pH of the final mineral suspensions was adjusted between 0.5 and 10. [ABSTRACT FROM AUTHOR]

The compounds we have isolated and characterized include plutonium(III) and plutonium(IV) bound by ligands with a range of donor types and denticity (halide, phosphine oxide, hydroxamate, amine, sulfide) in a variety of coordination geometries. For example, we have obtained the first X-ray structure of Pu(III) complexed by a soft donor ligand. Using a “one pot” synthesis beginning with Pu metal strips and iodine in acetonitrile and adding trithiacyclononane we isolated the complex, PuI[sub 3](9S[sub 3])(MeCN)[sub 2] (Figure 1). On the other end of the coordination chemistry spectrum, we have obtained the first single crystal structure of the Pu(IV) hexachloro anion (Figure 2). Although this species has been used in plutonium purification via anion exchange chromatography for decades, the bond distances and exact structure were not known. We have also characterized the first plutonium-biomolecule complex, Pu(IV) bound by the siderophore desferrioxamine E.In this presentation we will review the preparation, structures, and importance of previously known coordination compounds and of those we have recently isolated. We will show the coordination chemistry of plutonium is rich and varied, well worth additional exploration. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

To understand the environmental behavior of metals we must consider a tremendous range of phenomena, from simple individual reactions, such as ligand complexation and solubility equilibria, to quite complicated and collective processes, such as metal-mineral-microbial interactions. Because of pressing contamination problems at DOE sites and the paucity of relevant actinide chemistry knowledge, research is needed in this entire range of science. The determination and evaluation of key thermodynamic data for actinide species and the development of geochemical, hydrological, and environmental transport models are progressing. In contrast, we know almost nothing about how actinides interact with microorganisms. Ubiquitous microorganisms can absorb, reduce, oxidize, solubilize, or precipitate actinides, thereby affecting their speciation, solubility, bioavailability, and migration. These effects are due to both direct and indirect interactions, such as sorption to the cell wall and reaction with microbial byproducts, respectively. Our goal is to fully characterize specific microbial-actinide interactions, both to develop this area of fundamental research and to determine how the interactions may be exploited to affect environmental actinide mobility/immobility and remediation efforts. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We combined fundamental chemical studies, site-specific investigations, and geochemical modelling to evaluate the understanding of the environmental behavior of plutonium. Solubility studies were conducted in J-13 water from the Yucca Mountain site representing the range of natural waters of low ionic strength. In these waters, amorphous plutonium oxide/hydroxide and/or colloidal Pu(IV) dominated the solubility-controlling solid. X-ray absorption spectroscopy studies revealed the +IV oxidation state to be prevalent. Geochemical modelling showed that at neutral pH, the Pu solubility is controlled by the solubility of the Pu(IV) solid at Eh (the redox potential of the solution) <300 mV. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Plutonium is thought to exist mostly as very low soluble and/or strongly sorbed plutonium(IV) hydroxide and oxide species in the environment, and therefore, has low risk of becoming mobile or bioavailable. However, compounds that solubilize plutonium can significantly increase its bioavailability and mobility. We are examining the fundamental inorganic chemistry of actinides with one type of biogenic chelator, microbial siderophores, in order to understand how they could affect actinide biogeochemistry. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]